In various technical fields, seals of elastic variable hardness material are required, which by reason of their configuration or due to the properties of the material must be assembled from two or more components. This requirement arises in the case of sealing rings for pipe couplings and the like, needing a higher elasticity in one cross sectional zone and a higher degree of shape stability in another cross sectional zone.
In processing such materials, it is desirable to produce moldings from components in which in the first working step the components are manufactured partially consolidated and then in a further working step are connected with one another and hardened.
Composite materials of varying hardness such as the present invention are considerably superior to uniform materials as the harder layer resists hard sharp edges while the softer layer is considerably more resilient and yielding. This provides for a considerable reduction of damage due to crushing and fatigue while at the same time reducing the thickness of the material.
In spite of existing composite materials, there is a need in the marketplace for materials having greater impact resistance, longer working lives, lower weight and other positive properties.
The bonding of reinforced plastics as revealed in the prior art is generally accomplished with reactive multi-component thermal set systems such as peroxide, cured unsaturated polyester, polyol-polyisocyanate systems and epoxy systems. Such systems require precise metering of the components to obtain uniform performance and generally include toxic or sensitive compounds needing special precautions in handling.
Additionally, such systems have a finite open mold time requiring the mating of the bonded parts before the materials cure or advance to a non-bonding stage. Furthermore, such systems require the bonded parts to be held together mechanically for long periods of time until the systems have cured sufficiently to provide a strong bond and consequently require a cleaning or purging of the application equipment to avoid setting of the adhesives and equipment.
Hot melted adhesives such as the present invention overcome such disadvantages since they are single stream systems and are not sensitive to shock. The present invention develops bond strength simply by the passage of short amounts of time and does not require the long curing periods of mechanical fastening. Additionally, they do not present a problem caused by premature cure or set in the application equipment.
The hard crystalline segments in the present invention contribute tensile strength toughness and high temperature performance to the polymer seals. The soft amorphous or low melting segments of the seals contribute wetability, elasticity and rubber characteristics to the seals.
The concept of multi-layered plastic bonding structures is known as is the idea of combining pre-polymers to form a single bonding structure. See e.g. Martins, U.S. Pat. No. 4,443,518; Willett, U.S. Pat. No. 3,933,675; Fujiwara, U.S. Pat. No. 4,182,898; and Lindenmayer, U.S. Pat. No. 4,410,478. Nowhere in the prior art, however, is disclosed the combination of pre-polymers having the characteristics and strengths as found in the present invention. Neither is the method of bonding and forming the polymer seals of the present invention disclosed.